Increasing the accuracy of location estimates for wireless local area network (WLAN) and cellular enabled devices

ABSTRACT

The disclosed subject matter relates to a method and system for increasing the accuracy of a WLAN based position estimate using cellular positioning information. In some embodiments, the method can include determining a set of possible WLAN location solutions for a WLAN and cellular enabled device based on one or more WLAN access points, obtaining cellular measurements from at least one cell tower, and determining the best WLAN location solution from the set of possible WLAN location solutions using the cellular measurements. In one embodiment, the method can include using the cellular measurements from the at least one cell tower to provide a cellular based location estimate for the WLAN and cellular enabled device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior U.S. patent application Ser.No. 13/914,850, entitled, Methods and Systems for Determining LocationUsing a Cellular and WLAN Positioning System by Selecting the Best WLANPS Solution, filed Jun. 11, 2013, now U.S. Pat. No. 8,638,725, which isa continuation of U.S. patent application Ser. No. 12/485,588, entitled,Methods and Systems for Determining Location Using a Cellular and WLANPositioning System by Selecting the Best WLAN PS Solution, filed Jun.16, 2009, now U.S. Pat. No. 8,462,745, which claims the benefit under 35U.S.C. §119(e) of U.S. Provisional Application No. 61/061,853, filed onJun. 16, 2008, entitled “Integrated WLAN-Based and Cellular-BasedPositioning System,” each of which is herein incorporated by referencein its entirety.

This application is related to the following references:

-   -   U.S. patent application Ser. No. 12/485,591, filed Jun. 16,        2009, now U.S. Pat. No. 8,155,666, and entitled “Methods and        Systems for Determining Location Using a Cellular and WLAN        Positioning System by Selecting the Best Cellular Positioning        System Solution;” and    -   U.S. patent application Ser. No. 12/485,595, filed Jun. 16, 2009        and entitled “Methods and Systems for Improving the Accuracy of        Expected Error Estimation in Location Determinations Using a        Hybrid Cellular and WLAN Positioning System.”

BACKGROUND

1. Field

The disclosure generally relates to hybrid positioning systems and, morespecifically, to methods of integrating a wireless local area network(WLAN)-based positioning system (WLAN PS) and a cellular-basedpositioning system (CPS) to improve the accuracy of location estimates,increase availability of the positioning service to more users, and alsoto improve estimation of the expected error in a user's positionestimate.

2. Description of Related Art

In recent years the number of mobile computing devices has increaseddramatically, creating the need for more advanced mobile and wirelessservices. Mobile email, walkie-talkie services, multi-player gaming, andcall-following are examples of how new applications are emerging formobile devices. In addition, users are beginning to demand/seekapplications that not only utilize their current location but also sharethat location information with others. Parents wish to keep track oftheir children, supervisors need to track the locations of the company'sdelivery vehicles, and a business traveler looks to find the nearestpharmacy to pick up a prescription. All of these examples require anindividual to know his own current location or the location of someoneelse. To date, we all rely on asking for directions, calling someone toask their whereabouts, or having workers check-in from time to time toreport their positions.

Location-based services are an emerging area of mobile applications thatleverage the ability of new devices to calculate their currentgeographic positions and report them to a user or to a service. Examplesof these services range from obtaining local weather, traffic updates,and driving directions to child trackers, buddy finders, and urbanconcierge services. These new location-sensitive devices rely on avariety of technologies that all use the same general concept. Bymeasuring radio signals originating from known reference points, thesedevices can mathematically calculate the user's position relative tothese reference points. Each of these approaches has its strengths andweaknesses depending upon the nature of the signals and measurements andthe positioning algorithms employed.

Cellular-based positioning uses cell towers to determine the location ofa mobile or user device. Cell towers are identified with a uniqueidentifier in each cellular network in each country. Herein, the uniqueidentifies of cell towers is referred to as cell ID. The cell IDs can bestored in a reference database, accessible by the mobile or user device.In the reference database, the cell ID can be used to link that cell IDto a previously determined location for the cell tower having that cellID, where the location is also stored in the database. CPS can be basedon received signal strength (RSS), time of arrival (ToA), or timedifference of arrival (TDoA) from cell towers. Cellular-basedpositioning systems also can be based on the nearest neighbor technique,in which the entire service area is surveyed and a database of receptioncharacteristics of points in the service area is constructed. Thelocation of the survey points also can be logged, for example, by usinga global positioning system (GPS). By comparing the receptioncharacteristics of the mobile device with the surveyed points, thelocation of the mobile device can be determined. CPS can determine theposition of a mobile device through several methods, including receivedsignal strength and time of arrival.

CPS location determinations based on received signal strength use thereceived power of signals received from cell towers and triangulate theposition of the mobile device based upon the received power values. TheCPS based on received signal strength is not as accurate a system ascompared to WLAN PS. The accuracy of the CPS systems using receivedsignal strength is on the order of hundred meters, while the accuracy ofWLAN PS is on the order of tens of meters.

CPS location determinations based on TOA measure the time that cellularradio wave travels to get to the mobile device from the cell tower andcalculates the distance from the mobile device to the cell towers basedon that time. If travel time of the cellular radio wave is measuredcorrectly, the calculated distance from the cell towers can be accurateas WLAN PS, for example, up to ten meters. However, if the travel timeis not measured correctly, the error in the location estimate can behigher than WLAN PS, for example, on the order of hundreds of meters upto a kilometer. The TOA method's accuracy depends on estimating the timeof arrival of the cellular radio wave (as the name also indicates). In anormal operational environment of cellular network, the received signalis subject to multipath effect, which means the cellular receiver (ofthe mobile receiver) receives multiple copies of the transmitted signalreflected from the surroundings of the mobile device. These copies ofthe transmitted signal can arrive at slightly different times, and theselection of the signal which represents the distance between the mobiledevice and cell tower (or is the best estimate of distance) can be achallenge and an important part of the design of TOA based CPS. Further,there can be an option to consider all copies of the received signal andcalculate distance based on all of them. In this case, there will be aset of distances (between the mobile device and cell tower) which willbe passed to a trilateration module in the CPS (discussed herein). Thetrilateration module considers all the distance measurements from allthe cell towers and finds the most likely location of the mobile device.

In the discussion herein, raw CPS measurements from a cell tower aregenerally intended to mean received signal strength (RSS) and/or timesof arrival (TOAs) and/or time differences of arrival (TDOAs). Referencesto cellular data are generally intended to mean the unique address ofthe cell tower (like cell ID), one or more record(s) of its, one or morepower profile(s), and other attributes based on previous measurements ofthat cell tower. References to a CPS equation are intended to mean amathematical equation relating the CPS measurements and data to thelocation of the mobile device.

WLAN-based positioning is a technology which uses WLAN access points todetermine the location of mobile users. Metro-wide WLAN-basedpositioning systems have been explored by a several research labs. Themost important research efforts in this area have been conducted by thePlaceLab (www.placelab.com, a project sponsored by Microsoft and Intel);the University of California, San Diego ActiveCampus project(ActiveCampus—Sustaining Educational Communities through MobileTechnology, technical report #CS2002-0714); and the MIT campus-widelocation system. There is only one commercial metropolitan WLAN-basedpositioning system in the market at the time of this writing, and it isreferred to herein as the WPS (WiFi positioning system) product ofSkyhook Wireless, Inc. (www.skyhookwireless.com).

FIG. 1 depicts a conventional WLAN-based positioning system based onWiFi signals. The positioning system includes positioning software 103that resides on a mobile or user device 101. Throughout a particulartarget geographical area, there are a plurality of fixed wireless accesspoints 102 that transmit information using control/common channelsignals. The device 101 monitors these transmissions. Each access pointcontains a unique hardware identifier known as a MAC address. The clientpositioning software 103 receives transmissions from the 802.11 accesspoints in its range and calculates the geographic location of thecomputing device using the characteristics of the radio signals. Thosecharacteristics include the MAC addresses, the unique identifiers of the802.11 access points, the Time of Arrival (TOA) of the signals, and thesignal strength at the client device 101. The client software 103compares the observed 802.11 access points with those in its referencedatabase 104 of access points. This reference database 104 may or maynot reside in the device 101. The reference database 104 contains thecalculated geographic locations and power profiles of all access pointsthe system has collected. A power profile may be generated from acollection of measurements of the signal power or signal TOA at variouslocations. Using these known locations or power profiles, the clientsoftware 103 calculates the position of the user device 101 relative tothe known positions of the access points 102 and determines the device's101 absolute geographic coordinates in the form of latitude andlongitude or latitude, longitude, and altitude. These readings then canbe fed to location-based applications such as friend finders, localsearch web sites, fleet management systems, and an E911 service.

In the discussion herein, raw WLAN measurements from an access point aregenerally intended to mean received signal strength (RSS) and/or timesof arrival (TOAs) and/or time differences of arrival (TDOAs). Referencesto data are generally intended to mean the MAC address, one or morerecord(s) of it, one or more power profile(s), and other attributesbased on previous measurements of that access point. References to aWLAN PS equation are intended to mean a mathematical equation relatingthe WLAN PS measurements and data to the location of the mobile device.

A WLAN-based positioning systems can be used indoors or outdoors. Theonly requirement is presence of WLAN access points in the vicinity ofthe user. The WLAN-based position systems can be leveraged usingexisting off-the-shelf WLAN cards without any modification other than toemploy logic to estimate position.

FIG. 2 illustrates a conventional way of integrating WLAN PS and CPS,which consists of a WLAN PS 201 and a CPS 206 and a location combininglogic 210.

WLAN PS 201 and CPS 206 are stand-alone systems, and each can operateindependently of the other system. Thus, the result of each system canbe calculated independent of the other system. The estimated locationalong with the expected error estimation of each system can be fed tothe location combining logic 210. The expected error estimation is alsoreferred to as HPE (horizontal positioning error) herein. The nominalrate of location update of CPS 206 and WLAN PS 201 is once a second. Thelocation combining logic 210 combines the location estimates calculatedin the same second by both systems.

WLAN PS 201 is a conventional system which estimates the location of amobile device by using WLAN access points (WLAN AP). WLAN PS 201 caninclude a scanner of WLAN APs 202, a device to select WLAN APs 203, atrilateration module 204, and HPE estimation device 205.

WLAN scanner 202 detects WLAN APs surrounding the mobile device bydetecting the received power (RSS, received signal strength) and/or timeof arrival (TOA) of the signal. Different methods can be used to detectWLAN APs including active scanning, passive scanning, or combination ofpassive and active scanning.

The select WLAN APs device 203 selects the best set of WLAN APs toestimate location of the mobile device. For example, if ten WLAN APs aredetected and one AP is located in Chicago and the others are located inBoston, without any other information, the Boston APs are selected. Thisis an indication that Chicago AP has been moved to Boston. In theconventional system, the best set of WLAN APs is selected based ongeographical distribution of WLAN APs, in addition to correspondingparameters of WLAN APs, including received signal strength, signal tonoise ratio, and the probability of being moved.

Trilateration module 204 uses WLAN APs and corresponding measurementsand characteristics to estimate location of the mobile device. Receivedsignal strength or TOA measurements from a WLAN AP are used to estimatedistance of the mobile device to the WLAN AP. The aggregation ofdistance estimates from different WLAN APs with known location is usedto calculate location of the mobile device. Trilateration 204 also canuse a method which is called nearest neighbor, in which a location witha power profile similar or closest to the power reading of the mobiledevice is reported as the final location of the mobile device. The powerprofile of each WLAN AP or entire coverage area can be found in thecalibration phase of the system by detailed survey of the coverage area.

HPE estimation device 205 is a module which estimates the expected errorof the position estimate of the mobile device. The HPE or HorizontalPositioning Error is calculated based on previously scanned APs andtheir characteristics and also characteristics of the received signal asit was explained in co-pending Skyhook Wireless application Ser. No.11/625,450 entitled “System and Method for Estimating Positioning ErrorWithin a WLAN Based Positioning System,” the entire disclosure of whichis hereby incorporated by reference.

CPS system 206 can include a cellular scanner 207, trilateration device208, and the CPS HPE estimation module 209.

The cellular scanner 207 receives signals from one or more cell towersin view of the device, decodes the received signals, and measuresreceived signal strength (RSS) and/or time of arrival (TOA) and/or timedifference of arrival (TDOA) of the signals based on the approach takenin the trilateration module 208.

The trilateration device 208 uses measurements from cell towers toestimate the location of the mobile device. HPE estimation device 209estimates the expected error of the estimated location. The HPEestimation device 209 is conventional and calculates expected errorbased on geometry of the cell towers and signal quality of the receivedsignal from cell towers, for example C/N (carrier to noise ratio).

Location combining logic 210 receives simultaneous location estimatesand HPE estimates from WLAN PS 201 and CPS 206. Simultaneous locationestimations include estimations within one second of each other. Thelocation combining logic 210 reports one estimated location by selectingone WLAN or CPS estimate or by linearly combining them. For example,location combining logic might select the WLAN PS 201 estimate.Otherwise, it may report the CPS estimated location, it might report thefinal location based on an expected error, or it might report a weightedaverage of the estimated locations by both systems according to the HPE.

SUMMARY

The disclosed subject matter generally relates to hybrid positioningsystems and, more specifically, to methods of integrating wireless localarea network (WLAN)-based positioning system (WLAN PS) andcellular-based positioning system (CPS) to improve accuracy of locationestimates, increase availability of the positioning service to moreusers, and improve estimation of the expected error in a user's positionestimate.

Embodiments provide systems and methods of integrating a WLAN-basedpositioning system (WLAN PS) and a cellular-based positioning system(CPS). An integrated system refers herein to a system that combines theinformation and measurements from both systems in order to increase theavailability of the positioning service to more users to improve theaccuracy of the positioning estimates, as compared to each individualsystem working independently. The integration can occur at differentlevels from a high-level combination of location estimation provided byboth systems to the lowest level of integration of raw measurements fromboth systems and combining them to find the best estimate of thelocation of a user or a mobile device. The integration also includesusing information from one system to assist the other system so as toincrease the accuracy of the various estimates.

The disclosed subject matter relates to a method and system forincreasing the accuracy of a WLAN based position estimate using cellularpositioning information. In some embodiments, the method can includedetermining a set of possible WLAN location solutions for a WLAN andcellular enabled device based on one or more WLAN access points,obtaining cellular measurements from at least one cell tower, anddetermining the best WLAN location solution from the set of possibleWLAN location solutions using the cellular measurements.

In some embodiments, the method can include using the cellularmeasurements from the at least one cell tower to provide a cellularbased location estimate for the WLAN and cellular enabled device.

In some embodiments, the method can include determining the best WLANlocation solution from the set of possible WLAN location solutions usingthe cellular based location estimate.

In some embodiments, determining the best WLAN location solution fromthe set of possible WLAN location solutions using the cellular basedlocation estimate can include determining a distance between each of thepossible WLAN location solutions and the cellular based locationestimate, and selecting the best WLAN location solution based on whichof the possible WLAN location solutions is within an expected error ofthe cellular based location estimate.

In some embodiments, determining the best WLAN location solution fromthe set of possible WLAN location solutions using the cellular basedlocation estimate can include eliminating possible WLAN locationsolutions which are far from cellular based location estimate.

In some embodiments, the set of possible WLAN location solutions caninclude a WLAN access point cluster.

In some embodiments, the method can include weighing the WLAN accesspoint cluster according to the distance from each WLAN location solutionto the cellular based location estimate.

In some embodiments, the method can include selecting WLAN locationsolutions having a small distance to the cellular based locationestimate. In some embodiments, the small distance is on the order of ahundred meters.

In some embodiments, the method includes eliminating WLAN locationsolutions having a large distance to the cellular location solution. Insome embodiments, the large distance is on the order of tens ofkilometers.

In some embodiments, each WLAN location solution in the set of possibleWLAN location solutions can correspond to a location of a WLAN accesspoint.

In some embodiments, the method can include comparing the location ofeach WLAN access point to the known location of the WLAN access pointstored in a WLAN reference database, and if the location of the WLANaccess point does not correspond to the known location of the WLANaccess point in the WLAN reference database, determining that the WLANaccess point has moved.

In some embodiments, the method can include updating the known locationof the WLAN access point in the WLAN reference database to correspond tothe location of the WLAN access point.

In some embodiments, the cellular measurements can include the cell IDof the cell tower.

In some embodiments, the method can include accessing a cellularreference database containing cell tower reference locations for eachcell ID, comparing the cell tower reference location to the cellularbased location estimate, and if the cell tower reference location andthe cellular based location do not match, informing the cellularreference database that the locations do not match.

In some embodiments, the method can include updating the cellularreference database with the cellular based location.

In one aspect, the disclosed subject matter relates to a system forincreasing the accuracy of a WLAN based position estimate using cellularpositioning information. The system can include a positioning modulehaving a WLAN module for receiving information from one or more WLANaccess points and a cellular positioning module for obtaining cell towerinformation from at least one cell tower, logic located in the WLANmodule to determine a set of possible WLAN location solutions for a WLANand cellular enabled device based on one or more WLAN access points, andlogic located in the positioning module to use the cell towerinformation to determine the best WLAN location solution from the set ofpossible WLAN location solutions using the cell tower information.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a more complete understanding of various embodiments of the presentinvention, reference is now made to the following descriptions taken inconnection with the accompanying drawings in which:

FIG. 1 illustrates a high-level architecture of a WLAN positioningsystem;

FIG. 2 illustrates a system for a conventional system for integratingWLAN PS and CPS;

FIG. 3 illustrates a system for providing a WLAN PS and CPS integratedlocation solution, according to some embodiments of the disclosedsubject matter;

FIG. 4A illustrates an example of selecting a solution between possibleWLAN PS solutions using a CPS location estimate, according to someembodiments of the disclosed subject matter;

FIG. 4B illustrates an example of selecting a detecting moved accesspoints/access point clusters or cell tower IDs, according to someembodiments of the disclosed subject matter;

FIG. 5 illustrates a system for integrating a WLAN PS and a CPS in whicha CPS location estimate is provided to the WLAN PS to select the bestsolution, according to some embodiments of the disclosed subject matter;

FIG. 6 illustrates an example of selecting a solution between possibleCPS solutions based on a WLAN PS location estimate, according to someembodiments of the disclosed subject matter;

FIG. 7 illustrates a system for integrating a WLAN PS and a CPS andusing a WLAN PS location estimate to select a CPS location estimateamong possible CPS possible location estimates, according to someembodiments of the disclosed subject matter;

FIG. 8 illustrates a system for examining the location estimate anduncertainty provided by a WLAN PS against a CPS location measurements inorder to find the best estimate of the location of a mobile device,according to some embodiments of the disclosed subject matter;

FIG. 9 illustrates an example for increasing the accuracy of anestimation of expected error by using CPS and WLAN PS information,according to some embodiments of the disclosed subject matter;

FIG. 10 illustrates a system for increasing the accuracy of anestimation of expected error by using CPS and WLAN PS information,according to some embodiments of the disclosed subject matter.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the disclosed subject matter provide a method ofintegrating a WLAN-based positioning system (WLAN PS) and acellular-based positioning system (CPS) to create a hybrid positioningsystem. An integrated or hybrid system refers to a system which inputsthe measurements and location estimates from one system to anothersystem before location estimate to improve the accuracy of thepositioning and velocity and bearing estimates, and the accuracy ofexpected error estimate, as compared to each individual system workingindependently. The method of integrating a WLAN PS and CPS to create ahybrid positioning system can add CPS final estimates as another inputto WLAN PS and WLAN PS final estimations as another input to CPS. In oneembodiment, raw CPS measurements and raw WLAN PS measurements also canbe integrated to select the best set of measurement to increase theaccuracy of position estimate and HPE.

FIG. 3 illustrates a block diagram of a hybrid system of a WLAN PS 301and a CPS 306.

The CPS 306 functions in a similar manner as the CPS 206 shown in FIG. 2except that it is configured to receive a WLAN PS trilateration output313 and a location estimation output 314 from the WLAN PS 301 and alsoto provide CPS trilateration 311 results to the WLAN PS. The integrationof the WLAN PS trilateration and location estimation results with CPS306 changes the design of CPS trilateration device 308 and HPEestimation device 309. A conventional CPS might need to be modified toprovide the trilateration device's 308 results 311 outside of the CPSsystem.

This design change of CPS 306 after receiving WLAN PS information 313,314 is discussed in more detail herein.

The WLAN PS 301 functions in a similar manner as the WLAN PS 201 shownin FIG. 2 except that it is configured to receive CPS trilaterationoutput 311 and CPS location estimation 312 and to provide WLAN PStrilateration results 313. The integration of the CPS trilateration andlocation estimation results with the WLAN PS 301 changes the design ofWLAN APs selection device 303, trilateration device 304, and HPEestimation device 305.

This design change of WLAN PS 301 after receiving CPS information 311 isdiscussed in more detail herein.

Under one embodiment, the disclosed method integrates a WLAN-basedpositioning system (WLAN PS) and a cellular positioning system (CPS) inwhich the WLAN PS provides a set of possible locations of a mobiledevice, and the CPS provides a location estimate of the mobile device.Among the possible WLAN PS location estimates, the WLAN locationestimations which fit the CPS location estimate the best are selected asthe final set of position estimates for the WLAN PS and CPS enabledmobile device.

In WLAN PS, the mobile device can detect one or more WLAN access points(WLAN APs), which can be used as reference points to locate the mobiledevice. The WLAN access points are generally randomly distributed andmay move over time. Therefore, the WLAN positioning system applies aclustering algorithm to identify all the clusters of WLAN access pointsthat are detected by the end user. Once the APs have been identified andgrouped into clusters, the location of the device can be determined byusing either each AP separately or by using the clusters of APs.

A cluster of WLAN access points is a set of WLAN access points whereeach access point is in the coverage area of each of the other accesspoints. WLAN access points which are farther than a normal coverage ofan access point from the cluster are considered to be part of a newcluster.

Once the APs have been identified and grouped into clusters, thelocation of each cluster of WLAN APs is estimated. The location of eachcluster can be considered a possible location of the mobile device.Additionally, the CPS can provide a position estimate for the mobiledevice using cellular measurements from at least one cell tower. Bycombining WLAN PS and CPS position estimates, WLAN PS possible locationscan be rejected if the distance from the WLAN PS possible locations tothe CPS location estimate is an order of magnitude higher than accuracyof the CPS, where an exemplary accuracy of a CPS can be a few hundredmeters. For example, if the distance between the CPS location estimateand a WLAN PS cluster is tens of kilometers, that cluster of WLAN APscan be rejected. In some embodiments, the location of individual APs,instead of clusters of APs, also can be examined against the CPSlocation estimate. For example, if two clusters of APs are pointing toBoston, one cluster of APs is pointing to Chicago and the CPS locationestimate is in Boston, one of the APs pointing to Chicago or the clusterof APs pointing to Chicago can be examined against the CPS locationestimate.

The final location can be calculated based on the remaining WLANpossible solutions, i.e., the remaining clusters of WLAN APs.

For example, FIG. 4A shows a WLAN PS 401, which consists of five WLANaccess points 404. The WLAN access points form two clusters in thisexample, a first cluster 402 and a second cluster 403. Each cluster canbe used to estimate the location of the user device. CPS also detectstwo cell towers 405 and estimates a location for the mobile device 406.

If distance between possible solutions of the WLAN PS is on an order ofmagnitude higher than the coverage area of the detected cell towers inCPS, the location estimate or solution 406 of the CPS can be used toselect or eliminate WLAN AP clusters.

In this example, let us assume that cluster 402 and 403 are pointing todifferent cities like Boston and Seattle. The CPS location estimate 406is consistent with cluster 402, and cluster 403 is rejected. Therefore,cluster 402 is selected to calculate the user location. In someinstances, cluster 403 can be assumed to be moved or relocated toBoston. Because we know that the user's location is in Boston, we canassume that the user's device cannot be detecting using an AP inChicago. Therefore, the cluster 403 can be assumed to have beenrelocated to Boston; otherwise, the user in Boston would not bedetecting that access point. Further, the locations of the WLAN APs aretracked in one or more reference databases to which the user device hasaccess. The user device accessed the reference database to determinethat the WLAN APs reference location is Chicago. Because the user devicehas determined that the WLAN AP or cluster of WLAN APs have moved, theuser device can send a message to the reference database to update thedatabase to reflect that the new location of that WLAN AP or cluster ofAPs is Boston. The reference database can then be updated to reflectthat new location. (For more details on detecting moved access points,please see U.S. patent application Ser. No. 11/359,154, entitled“Continuous Data Optimization of Moved Access Points in PositioningSystems,” filed Feb. 22, 2006; the entire contents are herebyincorporated by reference.) Therefore, cluster 403 WLAN APs can beidentified as moved in the reference database, and their location isupdated. Therefore, clusters of WLAN APs which are not referring to thesame general location as the CPS estimated location can be considered tobe incorrect. In other words, the associated location of WLAN APs ofthose clusters can be considered to be inaccurate or stale, that is, theWLAN AP may have moved.

Under some embodiments, the disclosed method integrates a WLAN-basedpositioning system (WLAN PS) and a cellular positioning system (CPS) inwhich the WLAN PS provides one location estimate of a mobile device, andthe CPS provides one location estimate of the mobile device, and theconsistency between the WLAN PS and the CPS location estimates is usedto choose a WLAN PS location estimate. Note that there is only onelocation estimation reported by each WLAN PS and CPS.

FIG. 4B illustrates an integrated solution of WLAN PS and CPS, in whichWLAN PS 401 estimates a location 410 based on detected WLAN APs 412,which is far from CPS cell tower 414 location estimate 416. For example,if the WLAN PS locates the mobile device in Boston and the CPS locatesthe mobile device in Chicago, the discrepancy between WLAN PS and CPSlocation estimates indicate that either WLAN AP 412 has moved or CPSlocation estimate is not correct and the detected cell IDs have moved.

The WLAN PS can detect one or more WLAN APs. The WLAN PS extractsassociated information about each detected WLAN AP from a referencedatabase. The known WLAN APs (i.e., WLAN APs for which the referencedatabase has location information) are used to locate the mobile device.

CPS also can detect one or more cell IDs of cell towers and extractscell information for the detected cell IDs, for example, location andthe coverage size of the cell tower associated with that cell ID. Thedetected cell IDs can be used to estimate the location of the mobiledevice. The estimated location by CPS can be used to verify the generallocation of the WLAN PS estimated location.

If the CPS and WLAN PS location estimates are pointing to the samegeneral location (WLAN PS location estimate is within the expectedaccuracy of the CPS location estimate), the WLAN PS estimated locationcan be reported as final location of the mobile device. If the CPS andWLAN PS location estimates are pointing to locations that not in thesame general location, this can indicate that the WLAN APs have moved orthe associated location of the detected cell IDs are not correct.

Further, if a confidence of one of the location estimates reported byWLAN PS or CPS is high and it is higher than the other reportedlocation, the estimated location with the highest level confidence isreported as the final estimated location of the mobile device. Forexample, if the latest locations of cell IDs are provided by thecellular carrier and most probably are correct, the confidence to thelocation associated to cell IDs is very high. Then, the locationestimates WLAN system can be assumed to be incorrect. The discrepancybetween the measurements can be reported back to the correspondingreference database. The WLAN AP or AP cluster locations can be updatedin the corresponding reference database. If the confidence of eitherlocation is at the same level, then no location may be reported. Thisdetermination can be reported back to corresponding reference databasesas an indication of possibility of WLAN AP movement and also a change ofcell ID associated location information.

WLAN AP movement is estimated to occur more often than a change in thelocation of cell IDs. Therefore, in the case that WLAN PS and CPSlocation estimates are not consistent and distance between the estimatedlocations is an order of magnitude higher than the coverage of detectedcell towers, the CPS location estimate is considered as the finallocation estimate of the mobile device, and it can be assumed thatdetected WLAN APs were moved to the new location.

If it is detected that a WLAN AP was moved, the new location in whichthe WLAN AP was detected can be used to correct and update location ofthe WLAN AP in the reference database.

FIG. 5 illustrates block diagram of integrated solution of CPS and WLANPS. CPS 506 can be a standard, off-the-shelf device as discussed in FIG.2. The CPS location estimate result 312 is directed to selecting WLANAPs module 503 and trilateration device 504.

The WLAN APs selection devices 503 received the data from WLAN scanner202 and the CPS location estimate as an input. The WLAN APs selectiondevice 503 clusters WLAN APs based on the distance between the accesspoints and it results in one or more cluster. The clusters are used inthe trilateration device 504 to find possible location estimates of themobile device. The WLAN PS location estimates based on clusters areselected or rejected based on the cluster distance from the CPS locationestimate.

Under one embodiment, WLAN PS is used to detect and correct when thecell ID associated location is not correct and the cell ID has beenre-assigned to a cell tower with a different location. Cell towers aresubject to reconfiguration and change of their cell IDs. In a cellularnetwork, cell towers less often physically move and are more oftenreconfigured and the cell IDs are re-assigned. However, cellular networkreconfiguration happens rarely. When cellular networks are reconfigured,cell IDs may be re-assigned to another cell tower and the other celltower may not be in the same area as the original cell tower. This canresult in an incorrect location association for some cell IDs. If amobile device detects a set of reconfigured cell towers that still referto their old configuration with the old location of the towers, themobile device may find that the detected cell towers are an order ofmagnitude farther away than the normal coverage of a cell tower. Thenormal coverage of a cell tower is between couple of hundred meters tocouple of kilometers, but coverage of any particular cell tower can beestimated based on the density of cell towers or by site survey of thearea. Therefore, using different cell towers can result to differentlocation estimates. Thus, there are cases that the mobile device maydetect one or more cell towers with cell IDs whose associated locationsare not consistent with their recorded location in a reference database.In other words, the associated location of cell IDs point to differentlocations.

For example, if a mobile device detects five towers, two towers maypoint to Chicago and three others may point to Boston. In this case, theWLAN PS estimated location of the mobile device can be used to resolvethe discrepancy between cell IDs and location. In the example, if WLANPS location estimate is in Boston, it can be concluded that the cell IDspointing to Boston are correct and cell IDs pointing to Chicago are notcorrect. Thus, the WLAN PS location estimate can be used to identify ifthe cell IDs are pointing to an incorrect location and therefore havebeen re-assigned to a different cell tower.

If cell ID movement is detected, the location of WLAN PS can be used asa reference to correct and update location of the cell IDs which areregistered at an incorrect location in the reference database.

FIG. 6 shows CPS and WLAN PS, in which CPS results to two differentlocation estimates 605 and 606 and a WLAN positioning system 601 with alocation estimate 602. The detected cell towers 603 and 604 are farapart and resulting in two different location estimates 605 and 606. Inthis example, WLAN PS location estimate 602 is consistent with CPSlocation estimate 605. Therefore, it is concluded that the cell ID ofthe cell tower 604 was changed, and the cell ID of cell tower 604 islocated in the vicinity of the cell tower 603 and WLAN PS locationestimate 602.

FIG. 7 illustrates WLAN PS 801 and CPS 806 integrated solution, in whichall the modules are the same as FIG. 2, except for CPS trilateration808. Trilateration based on cell towers 808 also receives WLAN PSlocation estimate 314 as an input. When CPS trilateration 808 providesmultiple possible location estimates for the mobile device, the WLAN PSlocation estimate is used to detect cell towers having changed cell IDsand assigned to new locations.

Under another embodiment of the disclosed subject matter, a system andmethod is provided in which the WLAN PS can provide a region in which apossible location solution resides, and within the provided region thefinal location estimate of the mobile device can be selected based onCPS. This method can be used when the expected error of the CPS locationestimate is less than the expected error of WLAN PS location estimate.For example, when CPS uses TOA or TDOA technology and there is a line ofsight connection between the mobile device and the cell towers, theexpected error of CPS can be less than that of WLAN PS. When CPS usesTOA and TDOA technology, the arrival time of received signal from eachcell tower can be estimated. The received signal in cellular network canbe subject to multipath, and there can be multiple copies of thereceived signal. Therefore, there can be multiple choices for thearrival time of the signal, which can result in different distanceestimations between the mobile user and the cell tower. Thus, a set ofdistance measurements from two or more cell towers can result inmultiple possible location estimates for the mobile device. CPS possiblesolutions are combined or selected by additional location informationprovided by WLAN PS about the location of the mobile device. Forexample, the CPS solution closest to the WLAN PS location solution canbe selected as the final location estimate of the mobile device orpossible solutions of CPS can be weighted according to their distance tothe WLAN PS solution. After assigning a weight to each possible CPSlocation, various algorithms can be used to combine or select CPSpossible locations. For example, the final reported location can beweighted by an average of all possible locations, low weight locationscan be removed from the weighted average, or only the highest weightedlocation can be reported. Selection can be a special case of weighting,in which the respective weights are zero and one. A low weight cancorrespond to a CPS estimate that is far from the WLAN PS solution, forexample, on the order of hundreds of meters. A high weight cancorrespond to a CPS estimate that is close to the WLAN PS solution, forexample, within on the order of tens of meters.

In some embodiments, there is only a measurement from one cell tower.Therefore, only the distance from one cell tower is known, which resultsto a circle of possible solutions of cell positioning system, and thecellular based position estimate (in the circle of possible CPSsolutions) closest to the WLAN location estimate is selected as thelocation of the WLAN and cellular enabled device

FIG. 8 shows an integrated WLAN PS and CPS, in which WLAN PS 901provides an estimate of the location of the mobile device with someuncertainty 903. The uncertainty 903 can be the expected error of WLANPS. The mobile device also acquires signals from two or more cell towers902. CPS uses TOA in this example, and it returns a set of possiblelocation estimates 904, 905, and 906. The location estimate 904 can bethe final location estimate of the mobile device, because it isconsistent with WLAN PS location estimate 903.

Referring back to FIG. 7, FIG. 7 shows an integrated solution of WLAN PS801 and CPS 806 in which final location estimate 314 provided by WLAN PSis given to CPS trilateration device 808. However, in this embodiment,the CPS trilateration device 808 uses the WLAN PS location estimate 314to select the best CPS location estimate instead of using the WLAN PSlocation estimate 314 to determine if the cell ID has moved.

WLAN PS 801 is an off the shelf system. The CPS 806 and trilaterationdevice 808 can be modified to receive the WLAN PS location estimate 314as an input. When the distance between associated locations of at leasttwo detected cell IDs are an order of magnitude higher than normalcoverage of the detected cell towers, the WLAN PS location estimate 314can be used as an arbitrator to select cell IDs which are in the generalarea of the WLAN PS location estimate. Other cell IDs which are not inthe general area of the WLAN PS location estimate can be marked aschanged, i.e., the associated location of the cell tower was moved.Selecting the best set can mean selecting the one which is not moved. Inother words, best set can be the set which has not moved.

Another embodiment of the invention provides a method to increase theaccuracy of the expected error of a location estimate of an integratedlocation solution of CPS and WLAN PS and compare the integrated error toerror location results for each individual system. The expected errorestimation provides an uncertainty area around the estimated location.If the estimated locations of the WLAN PS and the CPS are within theuncertainty area of each other, i.e., the expected errors of the twosystems are consistent, the uncertainty area of the final estimate canbe reduced based on distance between estimated locations from bothsystems. If the estimated locations of WLAN PS and CPS are not withinthe uncertainty area of each other, i.e., the expected errors areinconsistent, the uncertainty area is increased based on distancebetween estimated locations from both systems. If only one of theestimated locations of WLAN PS and CPS falls inside the uncertainty areaof the other system, the uncertainty area can be reduced or increasedbased on the quality of estimated error from each system. The estimatederror of location estimate normally reports the 95% confidence interval,but it can report any other confidence interval as well.

FIG. 9 illustrates WLAN PS location estimation 1301, WLAN PS expectederror of estimation 1303, CPS location estimation 1302 and CPS expectederror of estimation 1304. The reported uncertainty by each system can bethe expected error of a final position estimate. The error of estimationalso can be referred to as uncertainty area.

In such a system, the CPS and WLAN PS each can provide a locationestimate and also an estimate of the expected error in that locationestimation. The expected errors of the location estimate provided byboth systems can be combined in order to provide a better estimate ofthe error of the location estimation. For example, if each systemprovides an area around the reported location as an uncertainty of theestimated location (1303 and 1304), the integrated system considers theoverlap of the uncertainty areas 1305 and also the distance betweenestimated locations 1306 to estimate the uncertainty of the finallocation estimate. The greater the distance between the estimatedlocations by CPS and WLAN PS is, the higher the expected error oflocation estimation. In another implementation, the system can selectthe location estimate with the lowest uncertainty as the final locationestimate.

FIG. 10 illustrates a block diagram of integrated WLAN PS and CPSsystem, in which the expected error of each system is calculated usingconventional methods, and the results are provided to integrated errorestimation system device 1411. The integrated error estimation 1411calculates the final expected error by considering the consistencybetween the reported locations by WLAN PS and CPS.

Upon review of the description and embodiments of the present invention,those skilled in the art will understand that modifications andequivalent substitutions may be performed in carrying out the inventionwithout department from the essence of the invention. Thus, theinvention is not meant to be limiting by the embodiments describedexplicitly above and is limited only by the claims which follow.Further, the features of the disclosed embodiments can be combined,rearranged, etc., within the scope of the invention to produceadditional embodiments.

What is claimed is:
 1. A method of increasing the accuracy of locationestimates for wireless local area network (WLAN) and cellular enableddevices, the method comprising: by a WLAN positioning system (PS),identifying at least one WLAN access point (AP) in signal range of aWLAN and cellular enabled device based on wireless signals received bythe WLAN and cellular enabled device transmitted by the at least oneWLAN AP, retrieving an estimated location of the at least one WLAN APstored in a reference database, and determining a WLAN-based locationestimate for the WLAN and cellular enabled device based at least in parton the estimated location of the at least one WLAN AP; by a cellularpositioning system (CPS), identifying at least one cell tower in signalrange of the WLAN and cellular enabled device based on cellular signalsreceived by the WLAN and cellular enabled device transmitted by the atleast one cell tower, the at least one cell tower having a cellidentifier (ID) associated with a location stored in the referencedatabase, and determining a cellular-based location estimate for theWLAN and cellular enabled device based at least in part on the locationassociated with the cell ID; comparing the cellular-based locationestimate to the WLAN-based location estimate to determine whether adistance between the cellular-based location estimate and the WLAN-basedlocation estimate exceeds a pre-determined threshold; and upon thecondition that the distance exceeds the pre-determined threshold,inferring that the location associated with the cell ID is inaccurateand updating the location associated with the cell ID in the referencedatabase, the updated location used in determining resulting locationestimates for the WLAN and cellular enabled devices.
 2. The method ofclaim 1, wherein the determining the cellular-based location estimatecomprises: determining a set of cellular-based location estimates ofwhich the cellular-based location estimate is a member, wherein theWLAN-based location estimate is consistent with at least one othercellular-based location estimate of the set of cellular-based locationestimates.
 3. The method of claim 1, wherein the resulting locationestimate for each of the WLAN and cellular enabled devices is based atleast in part on wireless signals received by a respective WLAN andcellular enabled device transmitted by at least one WLAN AP and cellularsignals received by the respective WLAN and cellular enabled devicetransmitted by at least one cell tower.
 4. The method of claim 3,wherein the at least one WLAN AP whose wireless signals are received bythe respective WLAN and cellular enabled device includes at least oneWLAN access point cluster of a plurality of WLAN APs, and wherein thereference database includes a plurality of estimated locationscorresponding to an estimated location of a plurality of WLAN APs in theat least one WLAN access point cluster.
 5. The method of claim 4,further comprising: weighting the at least one WLAN access point clusteraccording to a distance from a plurality of estimated locationscorresponding to the plurality of WLAN APs in the at least one WLANaccess point cluster to a cellular-based location estimate for therespective WLAN and cellular enabled device for use in determining theresulting location estimate for s the respective WLAN and cellularenabled device.
 6. The method of claim 5, further comprising selectingestimated locations corresponding to the plurality of WLAN APs in the atleast one WLAN access point cluster having a distance to the respectivecellular-based location estimate that is less than a pre-determineddistance, for use in determining the resulting s location estimate forthe respective WLAN and cellular enabled device.
 7. The method of claim6, wherein the pre-determined distance is on the order of a hundredmeters.
 8. The method of claim 1, wherein the pre-determined thresholdis an order of magnitude greater than a coverage area of the at leastone cell tower.
 9. The method of claim 8, wherein the pre-determinedthreshold is on the order of tens of kilometers away from the estimatedlocation of the at least one cell tower.
 10. The method of claim 1,further comprising updating the location associated with the cell IDstored in the reference database to correspond to the estimated locationof the at least one WLAN AP.
 11. The method of claim 1, wherein thecellular signals include the cell ID of the at least one cell tower. 12.A system for increasing the accuracy of location estimates for wirelesslocal area network (WLAN) and cellular enabled devices, the systemcomprising: a wireless local area network (WLAN) module for receivingwireless signals transmitted by at least one WLAN access point (WLANAP); a cellular module for receiving cellular signals from at least onecell tower; and logic configured to identify the at least one WLAN AP insignal range of a WLAN and cellular enabled device based at least inpart on the wireless signals, retrieve an estimated location of the atleast one WLAN AP stored in a reference database, determine a WLAN-basedlocation estimate for the WLAN and cellular enabled device based atleast in part on the estimated location of the at least one WLAN AP,identify the at least one cell tower in signal range of the WLAN andcellular enabled device based on cellular signals received by the WLANand cellular enabled device transmitted by the at least one cell tower,the at least one cell tower having a cell identifier (ID) associatedwith a location stored in the reference database, determine acellular-based location estimate for the WLAN and cellular enableddevice based at least in part on the location associated with the cellID, compare the cellular-based location estimate to the WLAN-basedlocation estimate to determine whether a distance between thecellular-based location estimate and the WLAN-based location estimateexceeds a pre-determined threshold, and upon the condition that thedistance exceeds the pre-determined threshold, infer that the locationassociated with the cell ID is inaccurate and update the locationassociated with the cell ID in the reference database, the updatedlocation used in determining resulting location estimates for WLAN andcellular enabled devices.
 13. The system of claim 12, wherein the logicconfigured to determine the cellular-based location estimate compriseslogic configured to: determine a set of cellular-based locationestimates of which the cellular-based location estimate is a member,wherein the WLAN-based location estimate is consistent with at least oneother cellular-based location of the set of cellular-based locationestimates.
 14. The system of claim 12, wherein the location associatedwith the cell ID is inferred to be inaccurate if the distance is anorder of magnitude larger than a coverage area of the at least one celltower.
 15. The system of claim 12, further comprising logic configuredto determine the resulting location estimate for each of the WLAN andcellular enabled devices based at least in part on wireless signalsreceived by a respective WLAN and cellular enabled device transmitted byat least one WLAN AP and cellular signals received by the respectiveWLAN and cellular enabled device transmitted by one or more cell towers.16. The system of claim 15, wherein the at least one WLAN AP whosewireless signals are received by the respective WLAN and cellularenabled device includes at least one WLAN access point cluster of aplurality of WLAN APs, and wherein the reference database includes aplurality of estimated locations corresponding to an estimated locationof a plurality of WLAN APs in the at least one WLAN access pointcluster.
 17. The system of claim 16, further comprising logic configuredto weight the at least one WLAN access point cluster according to adistance from a plurality of estimated locations corresponding to theplurality of WLAN APs in the at least one WLAN access point cluster to acellular-based location estimate for the respective WLAN and cellularenabled device for use in determining the resulting location estimatefor the respective WLAN and cellular enabled device.
 18. The system ofclaim 17, further comprising logic configured to select estimatedlocations corresponding to the plurality of WLAN APs in the at least oneWLAN access point cluster having a distance to the respectivecellular-based location estimate that is less than a pre-determineddistance for use in determining the resulting location estimate for therespective WLAN and cellular enabled device.